The present invention relates broadly to x-ray diagnostic systems, and in particular to a waveguide line spread function analyzing apparatus.
In the prior art, the method commonly utilized to measure the line spread function of x-ray diagnostic screen has made use of photographic film. This method evolved as the preferred method since most medical radiographs are usually made with a double emulsion film, sandwiched between two opposing x-ray fluorescent screens. Furthermore, the use of film provides the easiest way to access the fluorescent light trapped between the two screens.
This method of utilizing radiographic film and extracting the requisite information presents a complex problem. This is due mainly to the fact that the film is nonlinear and has a limited dynamic range. This necessitates two different exposures of the sandwiched film to test slit: one exposure to capture the peak of the impulse response within the film's linear range; the other to register its wings while the peak saturates the film. In conjunction with recording, the impulse response or accurate sensito-metric strip must be generated. This is normally accomplished via the inverse-square law, with corrections for air-path absorption.
Once all necessary exposures have been obtained, the film must be carefully processed. Controlled development is essential in studies where repeatable results are needed to more accurate measurements. Such close monitoring of the film processing condition is a difficult and tedious process. Furthermore, data reduction requires the use of a microdensitometer to read the negatives of the impulse responses and sensito-metric strip, and a computer for curve fitting, splicing, and smoothing in order to obtain an accurate exposure profile. In addition, corrections are needed for adjacency effects, direct grain exposure by x-rays, chemical spread function, specular density, and crossover. With due precaution and patience, it is possible to obtain accurate line spread function results for x-ray intensifying screens using film. However, the present invention utilizes a thick slab optical waveguide instead of film thereby providing a faster, more direct method of obtaining line spread function measurements of sandwiched screens.